1. Field of the Invention
The present invention relates to a pressure sensor provided with a joint and a diaphragm, and a manufacturing method of the same.
2. Description of Related Art
Various types of pressure sensors have been conventionally used in order to detect fluid pressure. Among pressure sensors, there is known such a pressure sensor that converts fluid pressure into strain through a diaphragm, and then takes out signals of the strain as changes of electrical resistance by means of a strain gauge on the diaphragm.
Downsizing, light weight, and low cost are demanded for the pressure sensors in the fields where high accuracy and high environmental resistance are required such as in vehicle applications and construction machinery applications.
A conventional pressure sensor is provided with a joint mounted on a pipe in which fluid to be measured flows and a diaphragm welded to the joint (for example, refer to Reference: Japanese Patent Laid-Open Publication No. 11-173930, FIG. 1, and FIG. 2).
FIG. 5 shows a schematic view of the conventional example.
Referring to FIG. 5, the pressure sensor is provided with a joint 101 made of stainless steel and a diaphragm 102 made of stainless steel, and a pressure guide hole 101A projecting in the axial direction is formed in the central portion of the joint 101. A step 101B is formed in the middle part of the joint 101.
The diaphragm 102 is arranged to detect pressure of the fluid introduced through the pressure guide hole 101A and includes a diaphragm body 102A on which a strain gauge (not shown) is formed and a tubular portion 102B formed on a peripheral edge of the diaphragm body 102A.
In assembling the diaphragm 102, an opening end of the tubular portion 102B abuts on an end face of the joint 101 and welding is performed while keeping the joining state. A welded portion 103 is formed along a periphery of the diaphragm 102.
According to the Reference, since welding is performed with a predetermined jig located close to a joint portion between the joint 101 and the diaphragm 102, the vicinity of the outer peripheral portion of the welding portion needs to be a space for welding. Also, the welded portion 103 needs a sufficient clearance in height from the step 101B of the joint 101 for welding operation.
Therefore, a pressure sensor requires the space around the joint 101 for welding the diaphragm 102 to the joint 101, which limits the downsizing of a pressure sensor.
Further, both of the joint 101 and the diaphragm 102 are made of stainless steel, which restricts weight reduction of a pressure sensor and yet incurs cost increase.